A031091 Position of n-th 3 in A031087.
3, 15, 33, 46, 48, 50, 51, 52, 54, 56, 58, 60, 62, 69, 87, 105, 123, 141, 162, 189, 216, 235, 238, 241, 243, 244, 247, 250, 253, 256, 259, 270, 297, 324, 351, 378, 405, 432, 459, 478, 481, 484, 486, 487, 490, 493, 496, 499, 502
Offset: 1